The objectives are to understand why the lupus immune system responds abnormally to nucleosomes, the major products of physiologically programmed apoptosis, and how can such autoimmune responses be specifically down-regulated? Identification of the dominant epitopes in nucleosomes critical for cognate interactions between autoimmune T helper (Th) cells and anti-DNA B cells of lupus provided us the essential tools for two novel discoveries leading to the proposed experiments. 1). It is widely believed that negative selection is intact in lupus. We have now found that the thymuses of lupus-prone mice are unable to delete transgenic thymocytes bearing nucleosome-specific T-cell receptor (TCR), although central tolerance for other antigens is intact. For the first time, mechanism/s of this peculiarly selective defect in central tolerance for nucleosomes in the lupus-prone thymus will be defined using new lines of TCR-transgenic mice we have generated. Mice of normal backgrounds bearing the transgenes will be studied first to define mechanism/s of negative selection of T cells specific for nucleosomes, the major products of ongoing apoptosis in the thymus, and to define the spectrum of negatively selecting epitopes. Novel mechanisms of peripheral tolerance in these new transgenic mice bearing lupus TCR will also be studied, particularly a functional uncoupling of signaling by autoimmune TCR from full T cell activation. 2). We have found that therapeutic tolerance with very low doses of select nucleosomal peptides can down-regulate active lupus by unique mechanisms. The critical epitopes that are recognized in MHC unrestricted manner by pathogenic autoantibody-inducing Th cells of lupus are also recognized by autoimmune B cells, and such shared epitopes are potent tolerogens for therapy. We will determine how pathogenic autoantibody inducing help is impaired by very low-dose vs. high-dose tolerance therapy with the nucleosomal peptide epitope/s we have identified, a). Role of anergy or deletion of lupus T and B cells; b). role of long-lasting regulatory (suppressor) T cell subsets with unique markers that are generated by peptide therapy; and c). the roles of tolerogenic dendritic cells and B cells in the generation of unusual regulatory T cells will be defined. The studies will address fundamental questions regarding autoimmunity and tolerance to an ubiquitous product of apoptosis, and would help in developing antigen-specific therapy of lupus.